This invention pertains to magnetic levitation (“maglev”) transportation systems and methods, and more particularly, those for suspending, guiding and propelling vehicles using magnetic forces.
The use of magnetic forces to suspend, guide and propel vehicles has been extensively researched and several full size demonstration prototypes have been built. In spite of proven advantages, such as fast, comfortable, quiet and efficient operation, maglev has been perceived as expensive and primarily suited for very high speed operation. Applications for urban use have been limited by the ability of proposed designs to compete effectively with conventional guided systems such as rapid transit, light rail, monorail, commuter rail and express busways.
Virtually all maglev designs that have been seriously considered for transportation applications can be characterized as either ElectroDynamic Suspension (EDS) or ElectroMagnetic Suspension (EMS). EDS designs use forces created by interaction of induced currents with the changing magnetic field that produced the currents while EMS designs use attractive force of a magnet to a ferromagnetic structure. Both EDS and EMS designs have been built and tested to the point where they are known to be viable to speeds of more than 150 m/s (336 mph, 540 km/h).
Each design has certain advantages and disadvantages. EDS has the virtue that it can operate with a larger magnetic gap than EMS but has the fundamental disadvantage that it creates high drag at low speeds and provides no suspension force when stopped. On the other hand, EMS has the advantage that it can operate very well at low speeds but has the disadvantage that the magnetic gap must be less than gaps that are practical with EDS designs.
The Japanese high speed test track has shown that an EDS system with a gap of 100 mm can achieve speeds of at least 150 m/s (353 mph) and the German Transrapid EMS test track has demonstrated reliable operation with a gap of 10 mm at speeds of 125 m/s (280 mph). For urban applications it appears that EMS has a major advantage and if the magnetic gap can be increased it would appear to have an even greater advantage for both low and high speed designs.
There is considerable prior art disclosed in existing patents and is instructive to review them in order to appreciate how the invention disclosed here is different from and an improvement on the prior art.
U.S. Pat. No. 3,638,093 (Magnetic suspension and propulsion system; James Ross; Issued Jan. 25, 1972) is an early example of a design that combines suspension and propulsion. This patent also references several of the important older patents dating to 1889. The design requires that power be transferred to the vehicle in order to propel it and the suspension requires substantial power because it does not use permanent magnets.
U.S. Pat. No. 3,842,751 (Transportation system employing an electromagnetically suspended, guided and propelled vehicle; Inventors: Richard Thornton, Henry Kolm; Issued: Oct. 22, 1974) shows how to use a single set of superconducting or permanent magnets to suspend, guide and propel a vehicle but is based on EDS technology so there is no necessity of controlling an otherwise unstable suspension. This design requires the use of wheels for low speed operation and because of the high low speed drag is not well suited to low speed operation.
U.S. Pat. No. 3,860,300 (Virtually zero powered magnetic suspension; Inventor: Joseph Lyman; Issued Jan. 14, 1975) shows how to use permanent magnets in a suspension system but the design is for a magnetic bearing and requires entirely separate structures for the permanent magnets and the electromagnets. It does not address the issue of guidance or propulsion.
U.S. Pat. No. 3,937,148 (Virtually zeros power linear magnetic bearing; Inventor: Paul A. Simpson; Issued: Feb. 10, 1976) shows how the U.S. Pat. No. 3,860,300 can be used for transportation applications but requires separate electromagnets and does not address the issues of guidance and propulsion.
U.S. Pat. No. 4,088,379 (Variable permanent magnet suspension system; Inventor: Lloyd Perper; Issued: May 9, 1978) builds on the ideas in U.S. Pat. No. 3,860,300 but it is not directly applicable to maglev using EMS.
U.S. Pat. No. 5,722,326 (Magnetic Levitation system for moving objects; Inventor: Richard Post; Issued Mar. 3, 1998) is a variation on U.S. Pat. No. 3,842,751 that uses Halbach arrays of permanent magents. It is specific to EDS and does not teach how to use permanent magnets in an EMS design.
The patents described above indicate the importance of the objectives of the patent disclosed here, but they leave out important ingredients.
In view of the foregoing, an object of this invention is to provide improved methods and apparatus for magnetic levitation (“maglev”), and more particularly, for suspending, guiding and/or propelling vehicles using magnetic forces.
Yet another object is to provide such methods and apparatus as result in reduced vehicle weight so that guideway, suspension and propulsion costs can be reduced.
Still another object is to provide such methods and apparatus as can operate, inter alia, with short headway and high speed so as to reduce both waiting time and travel time.
A related object is to provide such methods and apparatus as are economical to build.